1. Field of the Invention
The present invention relates to a method and apparatus for monitoring the effects of mechanical, chemical and biochemical cleaning techniques on the interior surface of pipelines.
When the water injection method is used in the recovery of crude oil from underground formations, it has been found that sulfate reducing bacteria (SRB) and general aerobic bacteria (GAB) grow on the interior surfaces of the system and produce a layer of biofilm. This biofilm produces adverse effects. First, the bacteria multiply within this layer and impede the flow of the water in the pipeline. Eventually the biofilm "sloughs" into the flow of the pipeline and is transferred to the formation where it interferes with the flow of water into the formation. Second, the interior surface of the pipeline is subject to corrosion which form under the biofilm and which can result in premature failure of the pipeline.
With water injection systems, two cleaning techniques used to reduce the corrosion and biofilm accumulation in the pipeline are chemical, or biochemical, and mechanical methods. In the first method, biocides, or bactericides, are injected into the pipeline. These bactericides kill the bacteria that forms the biofilm layer. In the second method, mechanical scraping is carried out to remove solids from the interior surface of the pipeline.
At present, little is known about the character of the biofilm, the parameters which effect the rate of biofilm build up, or the degree of corrosion that occurs under the biofilm layer. Likewise, little is known about the effects and impacts of either mechanical or biochemical cleaning techniques, their interaction with one another, or their cost effectiveness. For example, one variable that affects biofilm buildup and corrosion is the flow rate in the pipeline, and it is desirable for the purposes of evaluation to determine the effect of flow rate on the effectiveness of the cleaning techniques.
2. Description of the Prior Art
Various methods are known to the prior art for measuring the corrosive properties of a process stream or measuring the rate of corrosion of the inner surface of a conduit. U.S. Pat. No. 2,484,279 discloses a method for testing the corrosive properties of a process stream which employs a sidestream pipeline in which corrosion testing samples are suspended in the fluid flow. U.S. Pat. No. 2,083,011 discloses a device for determining the rate of corrosion of a conduit in which a removable plug made of the same material as the conduit is placed in a hole in the wall of the conduit. Upon removal of the plug its thickness is measured to determine the rate of corrosion of the plug and hence the rate of corrosion of the conduit itself.
However, the prior art does not provide methods or apparatus for monitoring the interior surface of a pipeline to determine the rate of corrosion and biological growth and the effect of various cleaning operations.
It is therefore an object of the present invention to provide a method and apparatus for determining the growth characteristics and corrosive effect of a biofilm on the inner surface of crude oil pipelines.
A further object of the present invention is to provide a method and apparatus for locally applying pipeline cleaning techniques, in the form of slugs of chemical treatment, such as bactericides, and mechanical scraping, so that their effects can be visually observed and quantitatively measured.
A further object of the present invention is to provide a representative method and apparatus for monitoring the nature of biofilm and the effects of pipeline cleaning techniques in which the flow of the mainstream pipeline is not interrupted.
Another object of the present invention is to provide a method and apparatus for monitoring the nature of a biofilm and the effects of pipeline cleaning techniques under various flow rates and conditions.
It is also an object of this invention to provide a coupon of improved design and apparatus for aligning and positioning the coupon in the pipeline.
A further objective of the present invention is to provide a method and apparatus for safely and conveniently monitoring the effects of pipeline cleaning techniques on pipelines that operate at high pressures.
A still further objective of the present invention is to provide means for monitoring the condition of the interior surface of a pipeline which will eliminate the possibility of oxygen ingress into the mainstream pipeline.